This invention relates to improved pressure responsive units, such as pressure actuated electrical switches.
In many hydraulic actuating systems, or other fluid handling apparatus, it is necessary or desirable to provide pressure responsive switches and the like at various locations for sensing and automatically responding in a predetermined manner to variations in the fluid pressure. These pressure responsive units are in most instances formed at least in part of a material which cannot effectively withstand the high temperatures encountered in the event of a fire in the vicinity of the equipment. For example, the body of the sensing unit may be formed of aluminum or other relatively low temperature melting material, and may melt completely down in the event of fire in a manner allowing free escape of the pressure fluid from the equipment. Such escape is particularly dangerous where the pressurized fluid is a highly flammable substance, such as gasoline, fuel oil, or the like.
In some instances, attempts have been made to provide fire resistance by forming the pressure responsive unit of high temperature resistant materials, such as stainless steel, or high strength alloys, or by utilizing temperature resistant welded construction or metallic sealing devices. However, most such approaches substantially increase the cost of the equipment, and in many cases impair the sensitivity or overall performance of the component.
The prior art also includes devices in which fusible elements have been employed for rendering a valve automatically closable in response to an increase in temperature, by virtue of melting of the fusible material to release the valve for closing movement. Such devices are shown in U.S. Pat. Nos. 3,245,423, 3,659,624, 3,842,853 and 3,896,835.